The present invention relates to a dry toner for electrophotography, and its production process as well.
A dry toner is usually produced by dispersing various agents such as releasing, coloring and charge control agents in a binder resin, grinding the resultant dispersion to toner size by fine grinding means, and classifying the powders into toner particles. Depending on the development system used, the dry toner is broken down into a one-component toner and a two-component toner comprising toner particles and carrier particles. A composite type toner is also known, in which the toner is coated thereon with a resin particle layer for the purposes of improving heat resistance, etc.
In recent years, faster operations and lower-temperature fixation than ever before have been required for electrophotography. To meet such demands, there are interal dispersion type oilless fixing toner particles wherein releasing agent particles are dispersed in a binder resin. However, it is required to prevent offsets such as particle deposition onto a fixing roller because of a decrease in the internal cohesive force upon melting of the binder resin. There is still no choice but to increase the content of the releasing agent. However, the incorporation of more releasing agent than required leads to a drop of the transparency of color toner.
For instance, JP-B 08-12451 discloses a toner composition production process, and Example 1 shows a toner composition consisting of 70% by weight of binder resin that is styrene-butadiene resin, 20% by weight of wax and 10% by weight of pigment. Referring to the shape of toner particles, the publication shows a toner particle comprising a continuous shell layer encapsulated with a waxy substance by heat treatment and less susceptible to produce frictional debris. However, it is expected that the encapsulating waxy substance contained in an amount of 28% by weight per 100 parts by weight of the binder resin causes process members such as photosensitive materials and developers to be contaminated by filming. Much wax offers a transparency problem.
JP-B 06-77161 discloses toner particles having uniform surfaces by xe2x80x9croundingxe2x80x9d ground and classified core particles by means of heat treatment, a jet mill, an impact mill or the like, and then uniformly fixing shell particles to the core particles by means of mechanical impact, and shows a process using an impact mill as an example. In the example, however, the shell particles are struck in, or otherwise simply fixed to, toner particles that are the core particles with a waxy substance or the like dispersed therein. Consequently, the shell particles are susceptible to detachment, offering several problems such as scattering in copying machines, contamination, image blurring, etc.
JP-B 08-12453 discloses a toner wherein micro-particles are deposited onto the surface of a suspension-polymerized core particle in water using a water-soluble polymerization initiator, and shows that by using micro-particles having a specific glass transition temperature or softening point and adding a releasing agent to the core particles, especially the micro-particles, it is possible to provide toners excellent in heat resistance, offset resistance and optical transmission and so well fit for color toners. Only by use of the micro-particles combined with the releasing agent, however, releasing agent particles remain partly at the surface of the toner particle, causing filming onto a photosensitive material and contamination of members in a developer. Thus, problems such as defective images or early member replacement remain still unsolved.
A primary object of the present invention is to provide an electrophotographic dry toner which prevents contamination by filming of process members such as photosensitive materials and developers and is improved in terms of offset resistance on fixation as well as robustness and transparency with a reduced amount of free fine powders, and so lends itself to a color toner in particular, and a process for producing the same.
According to the first aspect of the present invention, there is provided a dry toner for electrophotography comprising colored resin particles with releasing agent particles dispersed in a binder resin, characterized in that the releasing agent particles dispersed in each colored resin particle have a particle diameter distribution such that the particle diameter of releasing agent particles dispersed in the vicinity of the surface of each colored resin particle is larger than the particle diameter of releasing agent particles at a central site of the colored resin particle.
This dry toner for electrophotography is further characterized in that the aforesaid colored resin particles have an average particle diameter of 3 xcexcm to 10 xcexcm and a circularity of 0.93 to 0.99 and the releasing agent particles dispersed in the vicinity of the surface of each colored resin particle have a particle diameter of 0.05 xcexcm to 0.3 xcexcm.
According to the second aspect of the present invention, there is provided a dry toner for electrophotography comprising colored resin particles with releasing agent particles dispersed in a binder resin, and encapsulating resin particles fixedly fused to the surface of each colored resin particle to form a resin coating layer thereon, characterized in that the releasing agent particles dispersed in each colored resin particle have a particle diameter distribution such that the particle diameter of releasing agent particles dispersed in the vicinity of the surface of each colored resin particle is larger than the particle diameter of releasing agent particles at a central site of the colored resin particle.
This dry toner for electrophotography is further characterized in that the aforesaid colored resin particles have an average particle diameter of 3 xcexcm to 10 xcexcm and a circularity of 0.93 to 0.99, the releasing agent particles dispersed in the vicinity of the surface of each colored resin particle have a particle diameter of 0.05 xcexcm to 0.3 xcexcm, and the resin coating layer has a thickness of 0.05 xcexcm to 1 xcexcm.
According to the third aspect of the present invention, there is provided a dry toner for electrophotography comprising colored resin particles with releasing agent particles dispersed in a binder resin, and encapsulating resin particles fixedly fused to the surface of each colored resin particle to form a resin coating layer thereon, characterized in that each colored particle is coated with a resin coating layer with a releasing agent layer interleaved therebetween.
This dry toner for electrophotography is further characterized in that the aforesaid encapsulating resin particles are obtained by soap-free emulsion polymerization.
Furthermore, the dry toner for electrophotography is characterized in that the aforesaid resin coating layer has a thickness of 0.05 xcexcm to 1 xcexcm and the aforesaid releasing layer has a thickness of 0.001 xcexcm to 0.01 xcexcm.
Moreover, the dry toner for electrophotography is characterized in that the aforesaid binder resin has a flow softening point of 100xc2x0 C. to 150xc2x0 C., there is a difference of up to xc2x130xc2x0 C. between the softening point of the releasing agent and the flow softening temperature of the binder resin, and the flow softening temperature of the resin coating layer is at least 5xc2x0 C. higher than the flow softening temperature of the binder resin.
The process for producing the first dry toner for electrophotography according to the present invention is characterized by comprising the steps of adding 0.5 parts by weight to 10 parts by weight of a releasing agent non-compatible with a binder resin to 100 parts by weight of the binder resin and dispersing the releasing agent therein with a coloring agent added thereto, then grinding the resultant dispersion by fine grinding means into colored resin particles, and finally treating the colored resin particles in a hot-air stream for their re-dispersion so that the releasing agent particles dispersed in each colored resin particle have a particle diameter distribution such that the particle diameter of releasing agent particles dispersed in the vicinity of the surface of each colored resin particle is larger than the particle diameter of releasing agent particles at a central site of the colored resin particle.
The process for producing the second dry toner for electrophotography according to the present invention is characterized by comprising the steps of adding 0.5 parts by weight to 10 parts by weight of a releasing agent non-compatible with A binder resin to 100 parts by weight of the binder resin and dispersing the releasing agent therein with a coloring agent added thereto, then grinding the resultant dispersion by fine grinding means into colored resin particles, then uniformly fixing encapsulating resin particles onto the surface of the colored resin particles by mechanical impact or a dry mechanochemical method and finally treating the colored resin particles in a hot-air stream so that the encapsulating resin particles are fused onto the surface of the colored resin particles to form a resin coating layer thereon, and the releasing agent particles dispersed in each colored resin particle have a particle diameter distribution such that the particle diameter of releasing agent particles dispersed in the vicinity of the surface of each colored resin particle is larger than the particle diameter of releasing agent particles at a central site of the colored resin particle.
The process for producing the third dry toner for electrophotography according to the present invention is characterized by comprising the steps of adding 0.5 parts by weight to 10 parts by weight of a releasing agent non-compatible with a binder resin to 100 parts by weight of the binder resin and dispersing the releasing agent therein with a coloring agent added thereto, then grinding the resultant dispersion by fine grinding means into colored resin particles, then uniformly fixing encapsulating resin particles onto the surface of the colored resin particles by mechanical impact or a dry mechanochemical method and finally treating the colored resin particles in a hot-air stream so that the encapsulating resin particles are fused onto the surface of the colored resin particles to form a resin coating layer thereon, and the colored resin particles are coated with the resin coating layer with a releasing agent layer interleaved therebetween.
The process of producing the fourth dry toner for electrophotography according to the present invention is characterized by comprising the steps of adding 0.5 parts by weight to 10 parts by weight of a releasing agent non-compatible with a binder resin to 100 parts by weight of the binder resin and dispersing the releasing agent therein with a coloring agent added thereto, then grinding the resultant dispersion by fine grinding means into colored resin particles, then heating the colored resin particles in a hot-air stream at a temperature higher than the melting point of the releasing agent to form a releasing agent layer on their surfaces, and finally uniformly fixing encapsulating resin particles onto the surface of the colored resin particles by mechanical impact or a dry mechanochemical method.
The first, second and third dry toners for electrophotography according to the present invention and their production processes ensure to provide a toner which prevents contamination by filming of process members such as photosensitive materials and developers, and has improved offset resistance, robustness and transparency upon fixation. The dry toner for electrophotography obtained by the fourth production process of the present invention provides a useful color toner improved in terms of transparency with a reduced amount of free dust.